C-Forum

I picked up a Sub7 two-ball for a conversion. I'm going the fence rail route and need advice on seat position. Yesterday I took it to some flat water with a block of 4" foam on the rail for a temporary seat, just to get the for/aft position so I can order a spray skirt. At 4 inches from the back cockpit rim I felt too far aft, stern was too low. At 6 inches it felt balanced, bow almost pearled when I paddled forward pretty hard. I want to use the boat for combo playboat/river runner.
Called Snapdragon and they said they normally do C-1 skirts 8-9 inches from the rim.
I'm 6', 175. My only other boat has been an Atom, so I don't have much to reference.
Were my measurements completely out of wack?
Was my sense of "properly balanced" completely out of wack because of my experience in the Atom?
I'd appreciate any advice I can get!
Was Snapdragon out of wack and modern playboats have seat positions closer to the back rim?

A standard kayak tunnel is 6" forward.
I will start with my saddle position @ 8.5" from the rear of the cockpit rim and work forward or back in half inch increments.
With a conversion boat you have to focus on sitting up straight while taking paddle strokes as opposed to leaning forward to purchase the water in a long boat.
The 6" mark sounds like it will be stern heavy.

The base of the seatback in my converted Forplay is 8" from the outside rim of the cockpit aft. I feel like the trim is pretty good in this boat, for river running and play.

My Fipstick and H3 are both 9" from the outside of the rim

all from inside of cockpit rim...
Blunt: 8.5 inch
Delirious: 7 inch
s6x: 6.5 inch

Cheers, Jan

Tried it again, went with 7.5 when I ordered the skirt yesterday. We were measuring from the inside of the rim before, so that changed the number a bit also. Was glad to see Jan had a somewhat related boat at 6.5 from the inside rim.
Thanks for the help!